1 markMCQSection A

Select a pair of olfactory indicators from the following :

Acids, Bases and Salts

Indicators

Options

(a)Clove oil and vanilla essence

(b)Onion and turmeric

(c)Clove oil and litmus solution

(d)Vanilla and methyl orange

Official Answer

The correct option is (a) Clove oil and vanilla essence.

olfactory indicatorsclove oilvanilla essenceodour changes

Marking Scheme

11 mark

Hint

Recall the substances from Activity 2.2 whose characteristic smell changes or disappears when treated with an acid or a base.

Quick Oral Answer

Olfactory indicators are substances whose smell changes depending on whether they are mixed with an acidic or basic solution. Examples include onion, vanilla essence, and clove oil.

Analysis & Explanation

According to Activity 2.2 in the NCERT text, olfactory indicators are substances whose odour changes in acidic or basic media. The text identifies onion, vanilla essence, and clove oil as examples of olfactory indicators.

Option (a) is correct because both clove oil and vanilla essence are olfactory indicators.
Option (b) is incorrect because turmeric is a natural indicator that changes colour (turns reddish-brown in basic media), not an olfactory indicator.
Option (c) is incorrect because litmus solution is a natural dye indicator that changes colour (red in acid, blue in base), not an olfactory indicator.
Option (d) is incorrect because methyl orange is a synthetic indicator that changes colour, not an olfactory indicator.

Common Mistakes

1Students often confuse natural colour indicators like turmeric and litmus with olfactory indicators because they are also derived from natural sources.

Interesting Facts

Onion loses its characteristic smell when treated with a basic solution like sodium hydroxide ( $NaOH$ ), but retains it in acidic solutions, making it a highly reliable olfactory indicator.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2023?

This question carries 1 mark in the CBSE Class 10 Science 2023 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Acids, Bases and Salts" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Indicators" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2023 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2023 paper.